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COMMON: Use a prefix table to speed up the Huffman decoder

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Symbols for codes shorter than the prefix table index width are stored
in the table. All the entries in the table with an index starting with
the code are set to the symbol value. That way, when decoding it is
possible to get the number of bits corresponding to the table width from
the bitstream and directly find the symbol value. Longer code still need
to be searched for in the codes list.
This commit is contained in:
Bastien Bouclet 2019-04-08 19:24:00 +02:00 • committed by Filippos Karapetis
parent ae9eeb731f
commit 0f57aea2df
10 changed files with 123 additions and 165 deletions
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12
image/codecs/svq1.cpp
View file

@ -56,16 +56,16 @@ SVQ1Decoder::SVQ1Decoder(uint16 width, uint16 height) {
_last[2] = 0;
// Setup Variable Length Code Tables
_blockType = new Common::Huffman(0, 4, s_svq1BlockTypeCodes, s_svq1BlockTypeLengths);
_blockType = new HuffmanDecoder(0, 4, s_svq1BlockTypeCodes, s_svq1BlockTypeLengths);
for (int i = 0; i < 6; i++) {
_intraMultistage[i] = new Common::Huffman(0, 8, s_svq1IntraMultistageCodes[i], s_svq1IntraMultistageLengths[i]);
_interMultistage[i] = new Common::Huffman(0, 8, s_svq1InterMultistageCodes[i], s_svq1InterMultistageLengths[i]);
_intraMultistage[i] = new HuffmanDecoder(0, 8, s_svq1IntraMultistageCodes[i], s_svq1IntraMultistageLengths[i]);
_interMultistage[i] = new HuffmanDecoder(0, 8, s_svq1InterMultistageCodes[i], s_svq1InterMultistageLengths[i]);
}
_intraMean = new Common::Huffman(0, 256, s_svq1IntraMeanCodes, s_svq1IntraMeanLengths);
_interMean = new Common::Huffman(0, 512, s_svq1InterMeanCodes, s_svq1InterMeanLengths);
_motionComponent = new Common::Huffman(0, 33, s_svq1MotionComponentCodes, s_svq1MotionComponentLengths);
_intraMean = new HuffmanDecoder(0, 256, s_svq1IntraMeanCodes, s_svq1IntraMeanLengths);
_interMean = new HuffmanDecoder(0, 512, s_svq1InterMeanCodes, s_svq1InterMeanLengths);
_motionComponent = new HuffmanDecoder(0, 33, s_svq1MotionComponentCodes, s_svq1MotionComponentLengths);
}
SVQ1Decoder::~SVQ1Decoder() {

15
image/codecs/svq1.h
View file

@ -27,6 +27,7 @@
#include "image/codecs/codec.h"
namespace Common {
template <class BITSTREAM>
class Huffman;
struct Point;
}
@ -53,12 +54,14 @@ private:
byte *_last[3];
Common::Huffman *_blockType;
Common::Huffman *_intraMultistage[6];
Common::Huffman *_interMultistage[6];
Common::Huffman *_intraMean;
Common::Huffman *_interMean;
Common::Huffman *_motionComponent;
typedef Common::Huffman<Common::BitStream32BEMSB> HuffmanDecoder;
HuffmanDecoder *_blockType;
HuffmanDecoder *_intraMultistage[6];
HuffmanDecoder *_interMultistage[6];
HuffmanDecoder *_intraMean;
HuffmanDecoder *_interMean;
HuffmanDecoder *_motionComponent;
bool svq1DecodeBlockIntra(Common::BitStream32BEMSB *s, byte *pixels, int pitch);
bool svq1DecodeBlockNonIntra(Common::BitStream32BEMSB *s, byte *pixels, int pitch);